Translation of abstract (English)

Studies of Reactive Halogen Species (RHS) in the Marine and mid- Latitudinal Boundary Layer by Active Longpath Di erential Optical Absorption Spectroscopy The importance of reactive halogen species in the troposphere is on the one hand due to their strong e ect on tropospheric ozone levels, which has been discovered for the rst time during ozone depletion events in the polar boundary layer during polar sunrise. On the other hand recent eld and laboratory studies are indicating a great relevance of reactive iodine in new particle formation processes. Since particles in the marine atmosphere a ect the microphysical properties of stratocumulus clouds, they have a potential impact on climate. Within the framework of this thesis three eld campaigns using active longpath DOAS technique for studies of the reactive halogen species BrO, IO, OIO and I2 were conducted in di erent mid-latitudinal regions. Ground based measurements in the lower Arctic at the Hudson Bay yielded high levels of the BrO radical up to 35 ppt in the boundary layer, coinciding with nearly complete surface near ozone depletion. Two eld campaigns investigated the appearance of RHS in the coastal environments of the German North Sea and the French Atlantic Coast, IO was the only halogen oxide found in both locations with concentrations reaching 7.70.5 ppt. BrO in the marine boundary layer was estimated to remain below 1.5 ppt, neither OIO nor I2 could be identi ed in the spectra. Within a re-analysis of spectra taken during a former campaign in 1998 in Mace Head, Ireland 6112 ppt I2 were detected at night during extraordinary low water level most likely emitted by laminaria algae inhabiting parts of the lower intertidal zone.